tractor in a field pulling a planter
CORN YIELD: Besides planting date, yield potential also depends on stand establishment, heat units, moisture, disease, insect and weed pressure, and nutrient availability.

Figure out planting delay’s effect on yield

Corn Source: Planting date is only one of many factors that influence corn yield.

The 2018 planting season for corn can be officially called “delayed and condensed” in the state of Iowa. April brought cold and snow well into what is usually the early corn planting time for farmers creating many challenges. These challenges in the spring will affect corn hybrids and farming decisions throughout the entire growing season. But before the panic button is pressed, farmers must first evaluate how these planting delays will affect their crop yields.

This evaluation is important, to understand what can be realistically expected from corn yields before the plants begin growing in earnest and the summer season takes a toll on that yield potential.

The planting date of cornfields is a vital component in determining overall yield potential for the season. While farmers have been pushing the planting window for corn earlier and earlier, it is still normal to expect maximum yield potential in corn without an early April planting date.

Many factors help determine yield potential
The accompanying map shows the range of corn planting dates Iowa State University research has shown will result in 98% to 100% yield potential for corn hybrids. Even though farmers may be closer to the end of that planting window this season, the adverse effects will be minimal on pure potential for yield. It is important to note, however, that yield potential is not practical or actual yield.

This is the range in corn planting dates ISU research has shown will result in achieving 98% to 100% yield potential for corn hybrids. Source: ISU Publication IPM 1 “Corn and Soybean Field Guide”

Many factors will still drive down corn yields throughout the growing season, such as climate, insect pressure and disease. But starting with a chance at 100% yield potential is much more favorable than starting with only a maximum of 75% yield potential before anything else occurs. However, this spring there are many farmers who were not able to plant fields within the 98% to 100% yield potential dates.

Still potential for good yields
Many acres of corn across Iowa will go into the ground in May, with the potential for excellent yields still attainable. The accompanying chart shows the potential for corn hybrids planted later in the season, based on the planting populations used. This chart is a good reference to realistically see what farmers can expect out of a corn hybrid when planting stretches into mid- to late May and possibly even June.

Yield potential for corn planted later in the season decreases according to planting population. These values are based on ISU research and modeling; 100% yield potential is estimated to occur with 35,000 plant population. Source: ISU Publication IPM 1 “Corn and Soybean Field Guide”

This is also a useful chart if farmers need to make a replant decision based on early-season planting issues. By determining the corn replant date, farmers can see what potential the new planting will have compared to the original.

Every farmer would like a perfect planting season, but in Iowa we rarely get one. Tailoring your farming operation to the season at hand is the key to making sound economic farming decisions. Financial margins are tight in 2018, so managing inputs on fields that have a maximum potential for return is critical.

There are methods such as hybrid maturity adjustments, planting depth, population and fertilizers, which can assist in the field management of corn planted late. But they have little effect on overall yield potential. In general, corn needs time to grow, and there are no inputs that can effectively add more time to the calendar.

Witt is the ISU Extension field agronomist in west central Iowa. Contact him at [email protected].


Choosing corn hybrid maturity

What if corn planting is delayed into mid-to-late May? Should you switch to an earlier maturing hybrid or keep what you had planned for? Preliminary research indicates that in northern Iowa longer season hybrids can have a greater yield potential whereas hybrid maturity is much less influential on yield potential in central and southern Iowa regardless of planting date, assuming hybrids adapted to the area are used.

While there may be no benefit in yield potential to planting an earlier hybrid maturity, there can be risk management considerations. The main one is fall frost risk. For this reason, ISU recommends planting well-adapted maturities through May or early June planting dates. If planting gets delayed further, consider switching to earlier hybrid maturities to ensure crop maturity before fall frost occurs. An additional consideration would be to switch crops to soybeans if corn herbicides that have already been applied would not interfere with soybean germination and emergence.

Reminder: Check your stands when corn emerges, and scout for cutworms feeding on young plants. Some corn was planted this spring in soil that was too wet, which can have repercussions on plant and root growth. Sidewall smearing results in roots that are concentrated in the seed furrow. This leads to poor root growth, an increased risk of nutrient and moisture deficits and vulnerability of corn plants later in the growing season to be more susceptible to high winds.

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